Front-end Back-end Zimbra installation

I'm in the planning stages of my ZCS installation.
This is the configuration I would like to achive:

Zimbra (IMAP,POP,WEB, MTA) Proxy ---> Firewall ---> Zimbra Server

Zimbra Proxy will sit on a public subnet 169.1.2.3
Zimbra Server will sit on a private subnet 10.1.2.3

The idea is for users inside and outside the network to be able to pop or imap to their mailboxes.

Moreover, for both, the front-end proxy and the back-end Zimbra server, I will like to configure each on a 2 node RedHat Cluster for high availability.
So there will be a 2 node cluster for the proxy and another 2 node cluster on the backend for the zimbra server.

Could you point me to documentation I could read to achieve this?
Or if you can reply with some ideas on how to do this, that would be great too :-)